Defrost control for refrigeration systems



March 31, 1964 as. GEBERT 3,126,712

DEFROST CONTROL FOR REFRIGERATION SYSTEMS Filed Sept. 6, 1962 FIG. I

FIG. 2 21 INVENTOR.

GREGORY G. GEBERT BY 2y.

ATTORNEY.

United States Patent 3,126,712 DEFROST CONTROL FOR REFRIGERATION SYSTEMS Gregory G. Gebert, Woodstock, N.Y., assignor to Carrier Corporation, Syracuse, N .Y., a corporation of Delaware Filed Sept. 6, 1962, Ser. No. 221,756 6 Claims. (Cl. 62-81) This invention relates to air conditioning equipment and more particularly to air conditioning equipment including a refrigeration system operable under the reverse cycle principle to either heat or cool air for use Within an enclosure.

In air conditioning apparatus of the kind under consideration, a problem often encountered during operation of the apparatus on the heating cycle is the accumulation of frost on the heat extracting or absorbing coil. For example, in an air conditioning unit of a type adapted to be mounted in the window of a room to be supplied with the conditioned air, during cooling operation the high side of the refrigeration system is located outside the building and the low side is situated within the confines of the room. The heat rejected to a cooling medium such as air by the coil of the system functioning as the condenser flows, under the influence of a fan, through a path located wholly outside of the building.

To supply heat to the enclosure, the flow of refrigerant through the system is reversed so that the inside coil, functioning as the evaporator coil during the cooling cycle, operates as the condenser. In many cases the temperature of the outside coil functioning as the evaporator during the heating cycle falls below 32 F., the freezing temperature of water. It will be appreciated that under these circumstances the outside coil may acquire a substantial coating of frost in a relatively short period of time. This occurs when the moisture from the air flowing in heat exchange relation with the outside coil deposits on the surface of the coil and freezes.

Heretofore, it has been suggested that a defrost control arrangement operative under the influence of a timer mechanism be used to periodically initiate the defrosting action. Under these circumstances, at predetermined intervals and for a prescribed length of time the air conditioning unit is operated on a defrost cycle. A particular disadvantage of this arrangement is the institution of a defrost cycle of a predetermined length without regard for the condition of the coil.

To obviate this disadvantage thermostatic control of the timer in response to the temperature of the refrigerant in the coil to be defrosted has been suggested. However, this defrost control arrangement required additional circuitry and a relay with a resultant increase in cost and complexity.

It has also been proposed to employ a control responsive to the temperature differential between the outdoor air temperature and the outdoor coil temperature to institute a defrosting cycle. However, the efiicacy of this type of control is hampered by the extremely large tolerances inherent in this type of control. For example, in a temperature differential control operating on a 15 differential, that is a difference of 15 between outside air te. perature and outdoor coil temperature, the tolerance of the control is from 5 to 6. Thus, the outdoor coil of the unit might become frosted and operate at a low efficiency without defrost taking place or with an inordinate delay prior to initiation of defrost by the control. Alternately, defrost might be initiated prematurely again resulting in lower unit efficiency.

A chief object of this invention is to provide a novel defrost control arrangement operable to initiate defrost during operation of the air conditioning unit on the heating cycle.

3,126,712 Patented Mar. 31, 1964 It is an additional object of the present invention to provide a defrost control responsive to a preset refrigerant temperature in the outside coil occurring at a predetermined time.

It is a further object of the invention to provide a method of defrosting a heat transfer coil which is under the control of a timer modified by a temperature responsive element. Other objects of the invention will be more readily perceived from the following description.

This invention relates to an apparatus for cooling and heating an enclosure including a compressor, a first heat transfer coil disposed without the enclosure, :1 second heat transfer coil disposed within the enclosure to cool the same, a reversing valve for reversing the flow of refrigerant through the coils to interchange the heat transfer func tions of the coils to heat the enclosure, and control means for the apparatus including a first control responsive to a predetermined first enclosure temperature to energize the compressor to cool, a second control responsive to a predetermined second enclosure temperature to energize the compressor and the reversing valve to heat, timing means operable to periodically ready the reversing valve for deenergization, and means responsive to a predetermined first coil temperature during the ready period to deenergize the timing means and the reversing valve to defrost the first heat transfer coil.

The invention further relates to a method of controlling an air conditioning apparatus including a compressor, an indoor coil, an outdoor coil, and a reversing valve interconnected in refrigerant flow relationship in which the steps consist in energizing the compressor in response to a predetermined first enclosure temperature to cool, energizing the compressor and reversing valve in response to a predetermined second enclosure temperature to heat, periodically readying the reversing valve for deenergization, deenergizing the reversing valve in response to a predetermined first outside coil temperature during the ready period to defrost the outside coil while simultaneously ceasing the periodic readying of the reversing valve, and energizing the reversing valve in response to a predetermined second outside coil temperature to terminate defrost while simultaneously resuming periodic readying of the reversing valve for deenergization.

The attached drawings illustrate a preferred embodiment of the invention, in which:

FIGURE 1 illustrates schematically a refrigeration system of the type to which the invention applies; and

FIGURE 2 is a schematic diagram of the wiring circuit used with the invention.

The embodiment of the invention described pertains to an air conditioning unit of the room cooler type adapted to be positioned within a window of a building. The

unit is partitioned so that the compressor and a first heat exchanger coil are located without the building and a second heat exchanger coil is located within the building.

FIGURE 1 illustrates a refrigeration system of the type employed in conventional room units. A compressor 4 having a suitable drive motor 5 operatively connected thereto forwards high pressure vaporous refrigerant through line 26 to a reversing valve 12 in the path indicated by the solid arrows. The high pressure vaporous refrigerant travels from the reversing valve 21 through line 22 to the outside coil 6 wherein it is converted to the liquid phase by the circulation of air at ambient temperatures over the outside coil 6 by the fan 11. From outside I coil 6 liquid refrigerant flows through liquid line 24 to a restriction shown in the form of a capillary tube 9. While a capillary tube restriction has been shown, it is understood that other types of restrictions such as a constant pressure valve or a thermostatic expansion valve may be used in place of the capillary tube 9. The liquid refrigerant flows from the capillary tube 9 by means of line 27 to the inside coil 10. Air at room temperature is circulated over the inside coil 10 by the fan 3. The liquid refrigerant flowing through the inside coil 10 is vaporized by heat from the warm room air. The room air is accordingly cooled and is thereafter directed into the room to cool the same. The vaporous refrigerant formed in the inside coil 10 flows to the reversing valve 21 through line 25 and thereafter through suction line 26 to the compressor 4 to complete the refrigerant fiow circuit.

Inside fan 8 and outside fan 11 are driven by motor 7. Motor 7 is preferably a two speed motor. It is appreciated that fans 8 and 11 may be provided with individual drive motors in place of the common drive motor 7.

In order to supply the room with warm or heated air when the temperature of the air within the room or enclosure falls below that desired, refrigerant flow is reversed within the circuit described above through the action of the reversing valve 21. When the valve 21 is operated to provide flow of refrigerant in the path indicated by the dashed arrows the normal functions of the outside coil 6 and the inside coil 10 are reversed so that the air being circulated by fan 8 extracts heat from the refrigerant being circulated in the inside coil 10.

Moisture present in the atmosphere condenses on the surface of the outside coil 6 when the heat exchanged between the atmosphere and the outside coil is sufficient to lower the temperature of the air below its dewpoint. As noted heretofore, this moisture may, under certain circumstances, freeze on the surface of the outside coil 6 resulting in a layer of frost which may progressively build up on the outside coil. This accumulation of frost impairs the efficiency of the heat transfer action of the unit since the frost acts as a layer of insulation and restricts air flow. Accordingly, this invention provides an arrangement for removing this accumulation of frost.

This is accomplished by providing a control circuit effective to control the energization of the reversing valve of the unit. Included in the control circuit of the unit is a timing mechanism for periodically readying the control circuit to reverse the refrigerant flow and means responsive to a condition indicating the presence of frost on the outside coil during the ready period to reverse the refrigerant flow to initiate defrost, the frost responsive means simultaneously deenergizing the timing mechanism.

Referring more particularly to FIGURE 2 wherein the controlling circuits of the unit are diagrammatically represented, main power lines 39 and 31 furnish the primary source of power for the unit. Connected to the main power line is a manually operated switch 34 having an arm 35 arranged to selectively engage contacts 36 and 37. When the arm 35 is moved to engage contact 36, a circuit is completed through the two speed motor 7 which drives the inside and outside fans 8 and 11 respectively at high speed. Thus, if desired, the unit may be operated to circulate the air in the enclosure. Upon movement of switch arm 35 to a position in engagement with contact 37, the refrigeration system is prepared for energization.

A thermostatic switch 41, located within the area being conditioned, is connected to main power line 31. Thermostatic switch 41 is responsive to temperature conditions in the area being conditioned. Switch 41 functions to control the air conditioning unit to maintain a predetermined condition within the area in response to predetermined enclosure temperatures. As may be understood, if switch arm 35 of switch 34 engages contact 37, closure of switch 41 completes circuit 40 through the compressor motor 5 to drive the compressor 4.

Thermostatic switch 41 is provided with a pair of switch arms 42, 43 and two sets of interconnected contacts 44, 45 and 46, 47 respectively. Switch arms 42, 43 are adapted to engage either contacts 44, 45 or 46, 47 in response 4 to a demand for either cooling or heating as sensed by the thermostatic element to thereby close switch 41.

A circuit 50 including solenoid 51 controlling the operation of reversing valve 21 and switch 52 responsive to the temperature of the refrigerant in the outdoor coil interconnects contact 37 of switch 34 and contacts 46, 47 of thermostatic switch 41. Switch 52 may be any of the commercially available temperature responsive switches. Switch 52 is set to open and close at predetermined refrigerant temperatures, for example, to open at 30 F. and to close at 45 F. Switch 52 may be fixedly attached to the outside surface of outdoor coil 6 or to the refrigerant line leading thereto.

A second circuit 55 including a timing motor 56 and a timing motor controlled switch 57 interconnects the aforementioned contact 37 and contacts 46, 47. As is understood circuit 55 is in parallel relationship with the aforementioned circuit 50. Switch 57, normally closed, is periodically opened by the motor 56. As an example of the timing sequence, switch 57 may be opened once every fifty nine minutes for a period of one minute.

A circuit 66 interconnects the circuit 50 with the circuit 55. Circuit 60 includes manual switch 61 having rotatable switch arm 62 adapted to engage contacts 63, 64 of fan motor 7. Engagement of contact 63 by switch arm 62 readies the fan motor 7 for low speed operation while engagement of contact 64 by switch arm 62 readies the fan motor for high speed operation.

In operation, arm 35 of manually operated switch 34 may engage contact 36 to establish a circuit through fan motor 7 to operate the indoor and outdoor fans at high speed. In this position, the unit operates to ventilate the enclosure.

Assuming the temperature within the enclosure to be higher than the thermostatic switch setting, switch arms 42, 43 of thermostatic switch 41 will close contacts 44, 45 to ready the unit for cooling. The manual movement of switch arm 35 into engagement with contact 37 completes circuit 40 through the compressor motor 5 to drive the compressor 4. Switch 52, responsive to the temperature of the refrigerant gas in the outdoor coil 6, will be closed since the refrigerant gas temperature in the outside coil 6 now functioning as a condenser will be above the predetermined actuating temperature of the switch 52, for example, 30 F. If manual switch 61 is set to engage either of contacts 64 or 63 the fan motor 7 will drive indoor and outdoor fans 8, 11 respectively at either high or low speed. The unit will accordingly cool, it being understood that thermostatic switch 41 terminates the cooling upon a predetermined decrease in enclosure temperature. It is noted that fan motor 7 remains in operation at either high or low speed irrespective of the thermostatic switch 41 as long as switch arm 62 engages either contact 64 or 63 and switch arm 35 engages contact 37. As may be understood, the circuit may be modified to make the operation of fan 7 dependent upon and controlled by thermostatic switch 41.

Assuming a temperature in the enclosure lower than the temperature setting of the thermostatic switch 41, switch arms 42, 43 thereof will close contacts 46, 47 to ready the unit for heating. Actuation of manual switch 34 to close contact 37 completes circuit 40 through the compressor motor 5 to drive the compressor 4. If the temperature of the refrigerant gas in the outside coil is then above the predetermined actuating temperature of switch 52, for example, above 30 F., and switch 52 is assumed to be closed, circuit 50 is completed to energize solenoid 51 of reversing valve 21 to reverse the refrigerant flow to effect heating. Circuit 55 is also completed to energize timing motor 56. Fan motor 7 may operate indoor and outdoor fans 8, 11 respectively at either high or low speed dependent upon the setting of manual switch 61.

During heating operation, timing motor 56 periodically opens normally closed switch 57 for a short duration. It

may be noted that this periodic opening of switch 57 does not interrupt operation of the heating cycle as long as switch 52 remains closed; that is, as long as the temperature of the refrigerant in the outside coil remains above the lower setting of switch 52, for example, 30 F.

As heretofore described, operation of the unit on the heating cycle may result in the formation of frost on the outside or normally condensing coil (functioning now, however as an evaporator coil) under certain circumstances. The accumulation of frost impairs the efficiency of the coil with a resulting decrease in the temperature of the refrigerant passing through the coil. Should the temperature of the refrigerant fall below the low temperature limit of switch 52, for example, 30 F., closed switch 52 is opened. Switch 52 thereafter remains open until such time as the refrigerant gas temperature exceeds the high temperature setting thereof, for example, 45 F.

Although switch 52 may be opened by the temperature of the refrigerant in the outside coil falling below the predetermined low temperature limit of switch 52, the unit will continue to operate on the heating cycle if switch 57, which is periodically opened by the motor 56, is not simultaneously opened. Thus, although defrost switch 52 is open indicating a need for defrost, the unit will continue to operate on the heating cycle until such time as timing motor 56 opens switch 57. Upon the opening of switch 57 while the defrost switch 52 is open the circuit to the solenoid 51 of the reversing valve 21 is interrupted to initiate the defrost cycle. The circuits to the timing motor 56 and the fan motor 7 are also interrupted. Hot gas from the compressor flows directly to the outside coil 6 raising the temperature of the coil to a value suflicient to melt the frost from the surface of the coil. At a predetermined actuating temperature, for example 45 F., switch 52 will close to energize the solenoid 51 of the reversing valve 21 to initiate the heating cycle. Closure of switch 52 also completes the circuits 55 and 60 to energize timing motor 56 and fan motor 7, respectively. With the energization of timing motor 56, the timing motor driven switch 57 will close after the proper timing interval.

It will be appreciated that a defrost arrangement for a refrigeration system operative in response to the action of a timer mechanism regulated in accordance with the temperature of the refrigerant in the coil to be defrosted is provided. Other constructions embodying the invention will suggest themselves to those skilled in the art. It will be obvious that the operation of the various control arrangements may be varied without departing from the invention. Similar components may be arranged whereby the timer mechanism completes a circuit rather than interrupts it as shown.

While I have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In an apparatus for heating and cooling an enclosure including a compressor, an indoor heat transfer coil disposed within the enclosure, and an outdoor heat transfer coil disposed without the enclosure connected to form a closed path of flow for a refrigerant, and having means to reverse the flow of refrigerant through the coils to interchange the heat transfer functions of said coils to heat the enclosure, a defrost control comprising timing means operable periodically to ready said reversing means for deenergization, and means responsive to a first predetermined outdoor coil temperature during said ready period to deenergize said timing means and said reversing means to defrost said outdoor heat transfer coil.

2. An apparatus according to claim 1, said last mentioned means energizing said timing means and said reversing means in response to a second predetermined outdoor coil temperature.

3. In an apparatus for heating and cooling an enclosure including a refrigeration system having a compressor, an indoor coil and an outdoor coil, interconnected in refrigerant flow relationship, and reversing means for reversing the flow of refrigerant through the coils to interchange the heat transfer functions of the coils, the improvement comprising first control means responsive to a predetermined first enclosure temperature to energize said compressor to cool, second control means responsive to a predetermined second enclosure temperature to energize said compressor and reversing means to heat, said second control means including timing means operable to periodically ready said reversing means for deenergization, temperature responsive means operable to ready said reversing means for deenergization in response to a predetermined first outdoor coil temperature, said second control means being responsive to the simultaneous readying of said reversing valve by said timing means and said temperature responsive means to deenergize said timing means and said reversing means to defrost said outdoor coil.

4. An apparatus according to claim 3 in which said temperature responsive control means energizes said timing means and said reversing means to terminate defrost in response to a predetermined second outdoor coil temperature.

5. In the method of operating an air conditioning apparatus including an indoor coil, an outdoor coil, a compressor, and a reversing valve interconnected in refrigerant fiow relationship to condition an enclosure, the steps which consist in energizing the compressor in response to a first enclosure temperature to cool, energizing the compressor and reversing valve in response to a second enclosure temperature to heat, periodically readying the reversing valve for deenergization, deenergizing the reversing valve in response to a predetermined first outside coil temperature during said ready period to defrost the outdoor coil while simultaneously ceasing the periodic readying of the reversing valve, and energizing the reversing valve in response to a predetermined second outside coil temperature to terminate defrost while simultaneously resuming periodic readying of the reversing valve for deenergization.

6. In the method of operating an air conditioning apparatus having an indoor coil, an outdoor coil, a compressor and a reversing valve interconnected in refrigerant flow relationship and operable under the reverse cycle principle to condition an enclosure, the steps which consist in energizing the compressor in response to a predetermined first enclosure temperature to cool, energizing the compressor and reversing valve in response to a predetermined second enclosure temperature to heat, periodically readying the reversing valve for deenergization for a first period, readying the reversing valve for deenergization in response to a predetermined first outside coil temperature for a second period, deenergizing the reversing valve to defrost the outdoor coil at the simultaneous occurrence of said first and second periods while simultaneously ceasing the periodic readying of the reversing valve, and energizing the reversing valve in response to a predetermined second outside coil temperature while simultaneously resuming periodic readying of the reversing valve for deenergization.

References Cited in the file of this patent UNITED STATES PATENTS 2,847,833 Merrick Aug. 19, 1952 

5. IN THE METHOD OF OPERATING AN AIR CONDITIONING APPARATUS INCLUDING AN INDOOR COIL, AN OUTDOOR COIL, A COMPRESSOR, AND A REVERSING VALVE INTERCONNECTED IN REFRIGERANT FLOW RELATIONSHIP TO CONDITION AN ENCLOSURE, THE STEPS WHICH CONSIST IN ENERGIZING THE COMPRESSOR IN RESPONSE TO A FIRST ENCLOSURE TEMPERATURE TO COOL, ENERGIZING THE COMPRESSOR AND REVERSING VALVE IN RESPONSE TO A SECOND ENCLOSURE TEMPERATURE TO HEAT, PERIODICALLY READYING THE REVERSING VALVE FOR DEENERGIZATION, DEENERGIZING THE REVERSING VALVE IN RESPONSE TO A PREDETERMINED FIRST OUTSIDE COIL TEMPERATURE DURING SAID READY PERIOD TO DEFROST THE OUTDOOR COIL WHILE SIMULTANEOUSLY CEASING THE PERIODIC READYING OF THE REVERSING VALVE, AND ENERGIZING THE REVERSING VALVE IN RESPONSE TO A PREDETERMINED SECOND OUTSIDE COIL TEMPERATURE TO TERMINATE DEFROST WHILE SIMULTANEOUSLY RESUMING PERIODIC READYING OF THE REVERSING VALVE FOR DEENERGIZATION. 